As a technology for recording and reproducing digital data onto and from recording media, there has been provided a data-recording technology to be applied to optical discs used as the recording media. The optical discs to which the data-recording technology is applied include magneto optical discs. Examples of the optical disc are a CD (Compact Disc), an MD (Mini-Disc), and a DVD (Digital Versatile Disc). An optical disc is a generic name of recording media to which a laser beam is radiated to get reflected light in order to read out a signal representing changes in reflected beam. The optical disc is a disc-shaped recording medium made of a metallic thin plate protected by a plastic enclosure.
Optical discs are classified into two categories, namely, a reproduction-only type and a recordable type, which allows user data to be recorded on the disc. Examples of the optical disc pertaining to the reproduction-only category include a CD, a CD-ROM, and a DVD-ROM, which are already known. On the other hand, examples of the optical disc pertaining to the recordable category include those known as an MD, a CD-R, a CD-RW, a DVD-R, a DVD-RW, a DVD+RW, and a DVD-RAM. User data can be recorded onto an optical disc pertaining to the recordable category by adoption of recording techniques such as a magneto-optical recording method, a phase-change recording method, and a pigment-film-change recording method. The pigment-film-change recording method is also referred to as a write-once recording method, which allows data to be recorded only once and allows no overwriting of new data on already recorded data. The pigment-film-change recording method is suitable for an application to preserve data and the like. On the other hand, the magneto-optical recording method and the phase-change recording method allow new data to be written over already recorded data and are thus adopted in a variety of applications to record a variety of contents such as musical data, video data, game software, and application programs.
In addition, a high-density optical disc known as a DVR (Data & Video Recording) has been developed in recent years to drastically increase the storage capacity.
In order to record data onto an optical disc pertaining to the recordable category by adoption of recording techniques such as the magneto-optical recording method, the phase-change recording method, and the pigment-film-change recording method, it is necessary to provide a guiding means for carrying out tracking along a data track on the disc. For this reason, a groove is formed on the optical disc as a pre-groove. A groove or a land is then used as the data track. A land is a member resulting on the optical disc as an area sandwiched by two adjacent grooves. A land has a cross section with a shape resembling a plateau.
In addition, in order to be able to record data at any desired location on a data track, the address of each location on the data track needs to be embedded in the track. Such addresses are typically embedded in the data track by wobbling the groove serving as the track.
That is to say, a track used for storing data is formed in advance on the disc as a pre-groove with its side walls having wobbled faces to represent addresses.
By forming such a groove on the disc in advance, an address can be fetched from wobbling information conveyed by a reflected beam so that, even the address is not recorded on the track as pit data or the like, for example, data can be recorded and reproduced at a desired location on the track.
Thus, by adding address information embedded in a wobbling groove as described above, for example, it is no longer necessary to provide discrete address areas on the track as areas for recording address information as pit data so that the capacity of recording actual data can be increased by the sizes of the address areas, which become available for storing actual data.
It is to be noted that absolute time (address) information expressed by such a wobbling shape of a groove is referred to as an ATIP (Absolute Time In Pregroove) or an ADIP (Address In Pregroove).
By the way, management of defects on the optical disc is executed. This management is referred to simply as defect management.
The defect management is management for cataloging the address of each defect area. If spare recording areas are provided on the optical disc to each serve as a substitute for a defect area, the defect management is also management for managing addresses of the spare recording areas. A defect area is an area that data can no longer be recorded onto and reproduced from due to an injury or an other defect existing therein. The defect management is an important technique for preventing a failure from occurring in the system due to such an injury or a defect.
In the defect management, addresses of defect areas that data can no longer be recorded onto and reproduced from and addresses of spare recording areas are cataloged on a defect list. Thus, the defect list is a list used for cataloging information of importance to the defect management.
A high-density disc such as a DVR developed in recent years has a cover layer (a substrate) having a thickness of 0.1 mm in the dick thickness direction in its physical structure. In such a structure, phase-change marks are recorded and reproduced under a condition set by combining the so-called blue laser and an objective lens with an NA of 0.85. The blue laser is a laser beam having a wavelength of 405 nm. An optical disc with a diameter of 12 cm allows data of the amount of about 23.3 GB (gigabytes) to be recorded onto and reproduced from the disc provided that the data is recorded as phase-change marks on tracks with a track pitch of 0.32 microns and a line density of 0.12 microns/bit, a 64 KB data block is used as a recording/reproduction unit, and the disc has been formatted at a format efficiency of 82%.
A data zone on the optical disc is an area in which user data is recorded in and reproduced from. As a result of a formatting process of the optical disc, an area having a radius of 24 mm and a circumference having a radius of 58 mm becomes available as the data zone. An inner-side area enclosed by the circumference having a radius of 24 mm on the optical disc serves as a lead-in zone.
Used for storing defect management information, a defect management area is formed at a predetermined location in the lead-in zone. Two defect management areas may be provided. In this case, the two defect management areas are formed at predetermined adjacent locations in the lead-in zone.
A plurality of management areas such as, typically, two defect management areas, need to be formed because, if defect management information can no longer be read out from one of the two defect management areas for some reasons, the defect management information can still be read out from the other defect management area. With the two defect management areas formed at adjacent locations in the lead-in zone, however, it is quite within the bounds of possibility that defect management information can no longer be recorded and reproduced into and from both the two defect management areas when an injury is inflicted on the disc portion allocated to the two defect management areas. That is to say, the reliability of the defect management is not sufficient.
At a typical rotational speed of the optical disc, about 1.9 data blocks each having a size of 64 KB can be recorded onto a track on the circumference having a radius of 24 mm in one rotation of the optical disc.
The data zone used for recording user data has a large recording capacity of 23.3 GB. 18432 clusters in the data zone can be allocated as spare recording areas. Since such clusters have a size of about 1.207959552 GB, their size is only about 5% of the data zone used for recording user data. A defect list with a size of 8 bytes per entry will have a length of 147.456 KB and will occupy 3 clusters.
As described above, a defect management area including a defect list stored therein is formed as an area consisting of a plurality of clusters as described above. In this case, since about 1.9 data blocks each having a size of 64 KB can be recorded onto a track on the circumference having a radius of 24 mm in one rotation of the optical disc, with the two defect management areas formed at adjacent locations in the lead-in zone, it is quite within the bounds of possibility that defect management information can no longer be recorded and reproduced correctly into and from both the two defect management areas when an injury is inflicted on the disc portion allocated to the two defect management areas as explained above.